Vaccines are used to stimulate an immune response in an individual to provide protection against and/or treatment for a particular disease. Some vaccines include an antigen to induce the immune response. Some antigens elicit a strong immune response while other antigens elicit a weak immune response. A weak immune response to an antigen can be strengthened by including an adjuvant in the vaccine. Adjuvants come in many different forms, for example, aluminum salts, oil emulsions, sterile constituents of bacteria or other pathogens, cytokines, and so forth.
Cytokines are proteins made by cells that affect the behavior of other cells, and unlike many adjuvants, can modulate specific immune responses. One such cytokine is the interleukin-23 (IL-23), which controls inflammation in peripheral tissues by directing amplification and stabilization of T helper type 17 (Th17) cell populations. Th17 cells produce the pro-inflammatory cytokine interleukin-17 (IL-17), and are distinct from Th1 cells, which produce the pro-inflammatory cytokine interferon-γ (IFN-γ) and are induced by IL-12. Th17 cells are also distinct from Th2 cells, which are induced by interleukin-4 (IL-4). Th17 cells are distinct from Th1 cells and Th2 cells because Th17 cells activate inflammatory responses in both adaptive and innate immunity while Th1 cells activate T cell responses in adaptive immunity and Th2 cells activate antibody production in adaptive immunity.
Vaccines are also administered in many different ways (e.g., injection, orally, etc.) into many different tissues (e.g., intramuscular, intradermal, etc.). Not all delivery methods, however, are equal. Some delivery methods allow for greater compliance within a population of individuals while other delivery methods may affect the immunogenicity and/or safety of the vaccine. Accordingly, a need remains in the art for the development of safe and more effective adjuvants that increase antigenic responses irrespective of the identity of the antigen and route of administration.